It is conventionally known to use a foil bearing as a bearing for a shaft (or journal) that rotates at a high speed such as at tens of thousands rpm, in which the foil bearing comprises a plurality of foils (flexible membranes) for forming a bearing surface and supports the shaft by means of pressure of a fluid dragged in between the shaft and the foils as the shaft rotates. Such a foil bearing is disclosed in U.S. Pat. No. 4,465,384 issued to Heshmat et al., for example, in which a plurality of cooling air intake holes are formed in a sleeve (stationary mount member). Further, U.S. Pat. No. 4,818,123 issued to Gu has disclosed a foil bearing in which each foil is formed with a through-hole for allowing cooling air to flow therethrough from an outer peripheral surface to an inner peripheral surface of the foil.
Such foil bearings are being used in a wider industrial fields and it is desired to improve the durability of the foil bearing to allow a higher rotational speed and higher load. Even in the foil bearings disclosed in the above publications, it is still required to increase the cooling efficiency in order to achieve a higher rotational speed and durability in continuous operation because the frictional loss between the shaft and foils increases in proportion to the square of the rotational speed.